1. Field of the Invention
The present invention relates to a pointing stick device, and more particularly, to a pointing stick device that can effectively sense pressure from its cap.
2. Description of the Prior Art
A pointing stick device can control the movement and function of a cursor on a computer display. The pointing stick device is a common peripheral, used with both desktop and notebook computers. The cursor on the display can have three directions of movement: X, Y and Z. However, the pointing stick device can only control two of these directions, the X and the Y. Consequently, after setting the X and Y position of the cursor, the user must press a button to set the Z direction or to initiate a function.
It has grown increasingly important with pointing stick devices to increase the sensitivity in the X and Y directions, and add sensitivity in the Z direction. Sensitivity in the Z direction enables true 3-dimensional (3D) positioning of the cursor. The Z direction signal can also serve a button-like purpose, initiating functions. With the universality of 3D drawings and 3D animation, the prior art pointing stick device with only a 2-dimensional (2D) signal is no longer sufficient. Consequently, designing a pointing stick device with high sensitivity in the Z direction is very important.
Please refer to FIG. 1. FIG. 1 is a cross-sectional diagram of a prior art pointing stick device 10. The prior art pointing stick device comprises a column-shaped stick 12 for controlling the 2D movement of a cursor (not shown) on a display (not shown). The stick 12 comprises a top end 13, a bottom end 17 and a portion 15 between the top end 13 and the bottom end 17. The pointing stick device further comprises a cap 20 mounted on the top end 13 of the stick 12, a rubber cap 21 mounted on the cap 20 for the user""s convenience, a substrate 30 containing an aperture 36 for fixing the stick 12, a plurality of strain gauges 22 for sensing pressure and generating corresponding sensing signals, a plurality of leads 24 connected to the lower end of the strain gauges 22, a plurality of traces 32 installed on the substrate 30 and soldered to the leads 24 to transmit the sensing signals of the strain gauges 22, a collar 28 mounted around the bottom 17 of the stick, and a bonding compound 26 filling the gap between the collar 28, the stick 12 and the substrate 30 for affixing the bottom 17 of the stick into the aperture 36 of the substrate 30.
Please refer to FIG. 2 and FIG. 3. FIG. 2 is a schematic diagram of the pointing stick device 10 under an external horizontal force. The dashed center-line indicates the bending direction of the stick. FIG. 3 is a schematic diagram of the pointing stick device 10 shown in FIG. 1 under an external vertical force. The dashed center-line indicates the direction of compression of the force. When the user pushes the rubber cap 21, the cap 20 pushes the stick 12. The stick 12 undergoes bending deformation and the strain gauges 22 sense the induced pressure. The collar 28 helps the strain gauges 22 sense the bending deformation via the bonding compound 26. When the horizontal force (Fx, Fy) bends the stick 12, the strain gauges 22 generate bending strain signals Sx1, Sy1. When the perpendicular force (Fz) presses on the stick 12, the strain gauges 22 generate a compressive strain signal Sz1.
The inner side of the cap 20 of the prior art pointing stick device 10 is a column-shaped mouth 23 and the corresponding portion 15 of the stick 12 is also column-shaped. Consequently, the strain signal Sz1, which corresponds to the Z direction compression force, is too weak to be used. When the external force pushes the cap 20, the strain gauges 22 are compressed by the substrate 30, the collar 28, and the bonding compound 26, so they can only generate corresponding 2D strain signals Sx1, Sy1. Moreover, the bending stress of the stick 12 is limited, which limits the sensitivity of the strain signal in the horizontal direction. Also, during assembly of the pointing stick device 10, installation of the bonding compound 26 and the collar 28 is difficult, which increases costs.
It is therefore a primary objective of the present invention to provide a pointing stick device that can effectively sense the pressure from its cap to solve the above mentioned problems.
In a preferred embodiment, the present invention relates to a pointing stick device comprising:
a base plate;
a stick having a top end, a bottom end, and a middle portion between the top end and bottom end, the bottom end of the stick being vertically installed at the base plate;
at least one strain gauge installed around the top end for sensing pressure and generating corresponding sensing signal;
a cap mounted at the top end of the stick and having a cone-shaped mouth at its lower end for containing the top end of the stick; and
a base stand installed outside the middle portion of the stick and covering at least a portion of the strain gauge, a portion of the base stand being positioned inside the cone-shaped mouth of the cap;
wherein when an external force is applied to the cap, the force will be transmitted through the cone-shaped mouth of the cap to the portion of the base stand positioned inside the mouth and also to the strain gauge covered by the base stand wherein the strain gauge will sense the force from the cap and generate corresponding sensing signals.
It is an advantage of the present invention that it can provide a pointing stick device with increased sensitivity in the X and Y directions, and that can also effectively sense pressure in the Z direction from its cap.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description that is illustrated in the various figures and drawings.